Spinal cord stimulation requires a lead/stylet assembly that has a very high resistance to kinks and high buckling strength since the lead/stylet assembly is pushed through muscle, fascia and other tissue. The lead should preferably have a small diameter profile to facilitate ease of insertion into tissue. Because the lead has a small diameter, the stylet wire, by necessity, must also have a small diameter profile in order to fit inside the lead lumen. At the same time, the lead/stylet should preferably offer mechanical characteristics which enable multiple insertions into tissue, without breaking or permanently bending. Currently several types of lead-stylet assemblies exist for this purpose. An example of a stylet that engages the proximal end of the lead connector region in specified locations is the Pisces Quad Lead Model 3487A stylet available from Medtronic, Inc., Minneapolis, Minn., USA.
The location of the distal end of the stylet can potentially reside in different locations in the electrode region of the lead due to manufacturing tolerances in both the lead and the stylet. Manufacturing variability in the leads often requires the length of the stylet wires to be custom cut. Since the distal end of the stylet wire is typically prepared with a rounded tip that will not damage the lead during insertion, the stylet wire needs to be cut at the proximal end.
Stylet handles are typically overmolded onto the stylet wire or two half pieces are snapped over the stylet wire. These manufacturing techniques make it difficult to adjust the length of the stylet wire for different lengths and tolerances for these therapy delivery elements.